In a power save (PS) mode of a wireless local area network (WLAN) environment, when a frame to be transmitted to terminals, for example, stations (STAs) is buffered, an access point (AP) may periodically apply, to a traffic indication map (TIM), information indicating whether a buffered frame is present for each terminal, may insert the TIM into a beacon and then transmit the beacon. The TIM may include a bitmap. A single bit of the TIM corresponds to a single STA and corresponds to an association identifier (AID) that is mapped to an STA.
When buffered data to be transmitted to each STA is present, the AP may set, to “1” in the TIM, a bit corresponding to an STA to which the buffered frame is to be transmitted. An STA that is in a PS mode status needs to wake up in order to verify the TIM of the beacon.
When the buffered frame is verified from the TIM, an STA transmits a Power Save Poll (PS-Poll) frame or a trigger frame in order to obtain the buffered frame. However, when the number of buffered frames is large, many STAs may access a channel for a relatively short duration of time and thus, a collision may occur between the STAs.
For example, the TIM may include 2008 bits and indicate whether a buffered frame is present with respect to a maximum of 2007 STAs. Hundreds of bits may be set to “1” in the TIM. Additionally, when considering a sensor node, at least 6000 STAs may be associated with the AP.
Accordingly, there is a need for research on a technology that may minimize a collision between many STAs during a channel access process and also minimize an amount of power used by the STAs.